The invention relates to the separation and purification of plastics.
The production of plastics accounts for over $40 billion of annual product sales and more than 3% of the United States consumption of oil and natural gas. More than 90% of our production of these valuable materials is discarded. This is a considerable waste of natural resources and imposes an unwanted growing burden on people, cities, regions, agencies concerned with management and conservation of resources and pollution, and of course, ultimately on the environment. Improved collection, separation and reuse of plastics would tend to alleviate worsening of these burdens. If the collection, separation and reuse of plastics were sufficiently improved, plastics recycling could become one of the largest raw materials industries worldwide within a decade.
By generating over 80 billion pounds of material or $270 billion of production per year, and being responsible for approximately 3.2 million jobs, plastics and related businesses represent an extremely important materials industry to the United States. Unlike other material industries like steel and aluminum, however, this industry depends almost solely on new sources of raw material, most of it imported petroleum. This dependence becomes even more significant as the growth rate of plastics continues to outpace that of all other materials. Wasting this important material resource has significant international trade, economic and environmental implications.
The US produces almost 20 billion pounds per year of valuable engineering plastics for use in durable goods. These products are increasingly being collected and recycled at the end of their useful lives to avoid disposal costs and potential liabilities, and to recover metals and other marketable raw materials. The engineering plastics contained in these products are often one of the most valuable materials on a cost per pound basis, yet most of this valuable plastic resource is therefore landfilled, incinerated, or sent to Asia for recycling and reuse there.
Examples of the plastics recycling problem are evident in the case of so called xe2x80x98disposablexe2x80x99 plastic bottles and in durable goods. The main barrier to the recycling of a majority of bottles is that separation is limited to density-based systems which require significant pre-sorting by plastic type at Material Recovery Facilities (MRFs), leading to insufficient feedstock supply and poor economics. The main barrier to recycling of plastics from durable goods, such as automobiles, appliances, and computer and electronic equipment, is the multitude of plastic types and with different grades of the same type of plastic, often with overlapping densities, which must be separated. The re-use of such plastics, even if they can be separated, is often complicated by their degree of contamination, e.g. paint, metal film coatings and the like.
Embodiments may include one or more of the following advantages. The inventions enable the plastics to be separated from complex mixtures and recycled with high purities that result in higher market values. The recycling concept is certainly not new to plastics. Plastics have been recycled and reused since the beginning of their commercial use. Scrap and uncontaminated rejected parts generated from a manufacturing process are shredded and reused, typically back into the same application. As with other types of materials such as metal and glass, different types of plastics must generally be separated from one another to achieve high purity and consistent extruding or molding performance i.e., consistent physical properties typically verified by standardized ASTM tests (Izod impact, Deflection Test Under load (DTUL). Melt Flow Index (MFI) and the like) and higher market values.
Plastic types include acrylonitrile-butadiene-styrene (ABS), flame retardant (FR) ABS, ignition resistant (IR) ABS, acrylonitrile-styrene-acrylonitrile (ASA), high density polyethylene (HDPE), high impact polystyrene (HIPS), FR HIPS (a flame retardant HIPS), IR HIPS (an ignition resistant HIPS), low density polyethylene (LDPE), polyamide (PA), polybutylene terephthalate (PBT), polycarbonate (PC), PC/PBT (a blend of PC and PBT), PC/ABS (a blend of PC and ABS), FR PC/ABS (a FR blend of PC and ABS), polyethylene (PE), polyethylene terephthalate (PET), polymethyl methacrylate (PMMA), polyoxymethylene (POM), polypropylene (PP), polyphenylene oxide (PPO), polystyrene (PS), polyvinyl chloride (PVC), PVC/ABS (a blend of PVC and ABS), styrene acrylonitrile (SAN), styrene-butadiene rubber (SBR), styrene maleic anhydride (SMA), thermoplastic polyolefin (TPO), thermoplastic polyurethane (TPU), thermoplastic elastomer (TPE). Most plastics of different types are not compatible with one another, and while some commingled applications have been demonstrated, they capture much lower values than virgin plastic because the significant physical properties and characteristics are much less controlled, if at all, i.e. the plastics are of lower grade. With lower grade or lower purity products, the processing and performance flexibility afforded by purified single resin streams or compounded resin combinations (co-polymers) of consistent characteristics is lost.
As important, perhaps, is the ability to separate different grades of the same type (i.e., polymers built from the same monomer or monomers, but of different molecular weight, different ratios of monomers, different molecular morphology, different additive composition, concentration and the like) of plastic. Different plastic grades (i.e. plastics of the same type with a different range of properties) can have significant differences in important physical properties: e.g., medium impact, low gloss ABS and high-heat ABS.
Although an increasing number of bottles and rigid containers of all types are being recycled, a significant improvement in collection and reprocessing economics is needed for a majority of bottles to be recycled. Other types of plastics packaging (film, coatings, and closures) are recycled at a considerably lower rate than bottles. Durable goods (e.g. buildings, automobiles, appliances, and computer and electronic equipment) are gaining attention as a recycling opportunity as these types of products are increasingly being collected at the end of their useful lives by recyclers and manufacturers who recover useable components and metals. Although more plastic is actually used in durable goods than in packaging, technical barriers preclude their economical separation from these mixed material streams using conventional methods.
The problem of separating different polymeric materials from each other is the primary obstacle to economically recycling polymeric materials from durable goods, particularly when they have similar or overlapping density distributions. Durable goods are generally formed from a number of different types and grades of polymeric articles arranged as separate component sub-structures (pieces or parts) combined or attached into a unitary item, e.g., a computer monitor with a case of one material having several other sub-assemblies attached by glue, molding, or fasteners and the like.
Most plastic parts coming from durable goods streams contain unique challenges that are not met by the automated conventional plastics cleaning and sorting processes developed for packaging materials. The principle practice today for the recovery of highly contaminated scrap is hand-separation, which is cost prohibitive in most cases. The challenges in recycling plastics from durable goods include:
The plastics used in durable goods are more specialized than those used in packaging. Whereas the majority of plastic packaging can be categorized in five grades of plastic resin, more than fifty plastic resin grades might be required to comprise a similar fraction of the durables market. For example, while the PET plastic used to make a soda bottle may also be appropriate for a water bottle, the acrylonitrile-butadiene-styrene copolymer (ABS) used to make a computer housing is very different from the sort used in a refrigerator door, which is different again from that used in an automobile. This broad variety of materials increases the difficulty of separation.
In addition to different plastic types, many parts contain a wide variety of reinforcements, fillers, and pigments. Changing filler content and foaming agents causes material density to vary even within the same type of plastic.
Durable plastic parts often contain high levels of metal contamination, including wiring brackets, structural pieces, and molded-in screw inserts.
Paint and metallic coatings (i.e., contamination) on some parts make identification, sorting, and melt reprocessing much more difficult.
Larger and more variable thickness (i.e., parts having widely differing morphology) wall sections, increases the challenges associated with size reduction and particle size and shape control.
The apparent density of a plastic can be different from the intrinsic density of the plastic especially when the plastic is xe2x80x9cfoamedxe2x80x9d. A foamed plastic includes small bubbles or voids. The apparent density is often lower than the intrinsic density because it includes a contribution from encapsulated voids or vapor bubbles within material.
This invention relates to modifying the density or apparent density of polymers, particularly polymers in a mixture of different polymers or polymer grades, to effect purification and separation.
The invention relates to the separation and purification of plastics. Specifically it is related to apparatus and methods of separating a selected one or more members (selected plastic) of a mixture consisting of divided plastics and partitioning the selected member(s) into respective containers or output product streams separated from the balance of the mixture and from each of the other selected members.
The invention also relates to apparatus and methods for providing separated and partitioned output product streams (or separated containers) of individual types or grades of divided plastic by separating and partitioning plastics received from input recycling product streams of different types and grades of bulk plastic articles obtained from industrial and consumer product waste streams.
The invention specifically relates to mixtures that include a set of discrete members of divided polymeric materials of different types and/or grades. The divided polymeric materials may be prepared by dividing substantially larger formed and shaped articles made essentially from a single type or grade of plastic to enable separation or purification of one or more of the selected members from the mixture, especially a mixture of polymeric materials which is initially inseparable. The materials are typically divided (e.g., shredded, granulated, or ground) into discrete particles, flakes, shreds, i.e., free flowing. It would be advantageous to provide plastics recycling plants capable of handling mixed post-consumer plastic. When commercialized, similar plants could have a throughput comparable to large virgin plastic production facilities. Plastics could be recovered for reuse in similar or other applications. Plants could be built to accept shredded or baled mixed-rigid plastic containers or durable plastic goods. This could eventually make sorting of plastic waste at curbside unnecessary and lead to increased utilization of other waste materials such as paper, metals and glass by complementing the economics of their reuse.
Accordingly, several objects and advantages of the present invention are:
to provide a means of altering or shifting the apparent density of a polymeric material without degradation of the material;
to provide a means of altering the difference in apparent density between two discrete polymeric materials in such a way as to enable the separation of the two discrete polymeric materials;
additionally to provide a means of retaining the altered difference in apparent density between two discrete polymeric materials in the absence of the action or agent inducing the alteration;
to provide differentiation of polymeric material(s) within a mixed stream;
to provide a way of separating different component(s) of a mixed plastic stream based upon apparent density or specific gravity;
to provide a way of recovering purified plastic types from mixed streams containing different plastic materials;
to provide a way of improving the purity of a polymeric material by removing plastics;
to provide a plastic density differential alteration system and process i.e. differential plastic xe2x80x9cfoamingxe2x80x9d, for separating HIPS and ABS from appliances and unfoamed PC, PC/ABS, IR-HIPS, FR-HIPS, FR-ABS, and IR-ABS from computer and business equipment by shifting the density of one of the plastics by at least 0.03 g/cc;
to provide a separation process and system incorporating the differential density alteration process in combination with a de-foaming system and process for separating foamed PC, PC/ABS, PPO, IR-HIPS, and IR-ABS by selectively narrowing the density distribution for a given plastic by a considerable fraction;
to provide an alternative differential attribute alteration process to separate plastics based on differential morphology (e.g. thickness) alteration of different grade or type plastic chips having an initially uniform aspect;
to provide an integrated Material Recovery Facility combining one or more of the embodiments of the present invention into a overall recycling process for each or any of the following post-consumer sources: bottles and rigid containers, appliances, computer and electronic equipment (ESR), and automobiles (ASR);
to enable design, construction and operation of Material Recovery Facilities that provide throughputs of several multiples of conventional bottle recycling plants that have acceptable product quality;
to provide a means to alleviate broadening and overlap of the density distributions of different polymers in a mixture caused by size reduction;
to provide a plastic attribute (e.g. density) differential alteration responsive to a physical action (e.g. heat) in which the resulting material becomes separable;
For particular mixes of different grades and/types of mixed polymer waste streams (the input feedstock). Sets of procedures and criteria are established for a broad range of separation technologies, one or more of which can be selected to work for each particular separation which must be effected. The most effective combination of technologies can be incorporated into a final large scale advanced Material Recovery Facility (MRF) for commercial use.
The actual configuration of particular unit operations incorporating embodiments of the present invention within a given advanced Material Recovery Facility can be based on selected criteria of anticipated ease of use and economics. The innovations associated with these end configurations are discussed below.